diff --git a/include/__refstring b/include/__refstring
index 6866bf1..61ccc75 100644
--- a/include/__refstring
+++ b/include/__refstring
@@ -13,7 +13,7 @@
 #include <__config>
 #include <cstddef>
 #include <cstring>
-#if __APPLE__
+#ifdef __APPLE__
 #include <dlfcn.h>
 #include <mach-o/dyld.h>
 #endif
@@ -49,7 +49,7 @@
         return data + sizeof(*rep);
     }
 
-#if __APPLE__
+#ifdef __APPLE__
     static
     const char*
     compute_gcc_empty_string_storage() _NOEXCEPT